Estrogen-sensitive neurons are present in the brain of adult rats with the highest density of estrogen-concentrating cells in the preoptic area, hypothalamus and the amygdala. Estrogen has been found to be concentrated within the cell nucleus. This suggests that the primary mode of action of the hormone might be through the genome. Recently, through the use of inhibitors of RNA and protein synthesis, steroid induced sexual receptivity has been reversibly blocked; the inhibitors were given systemically. The aim of the present proposal is to study the mechanism(s) by which the steroid hormones facilitate sexual receptivity and induce ovulation in the intact cycling rat. Our experimental approach involves the intracranial injection of cycloheximide (CHX), an inhibitor of protein synthesis, into discrete brain areas implicated in the control of sexual behavior and ovulation. After injection of CHX, we will examine gonadotropin and steroid levels, ovulation and sexual receptivity. autoradiography and electron microscopy will be used to ascertain the amount of diffusion away from the injection site. Labelled amino acids will also be used to directly assess intracranial protein synthesis.